CRTs and other obsolete electronics account for a significant and rapidly increasing share of the solid waste generated by many different societies. From current estimates of 75,000 tons per year, the volume of this waste was expected to reach as much as 300,000 tons annually by 2005. The already increasing rates of discard will be exacerbated by the disposal of older units in favor of emerging technologies such as flat panel screens, high definition television (HDTV) and DVD players.
A cathode ray tube (“CRT”) is the main component in older televisions and computer monitors. The CRT is a specialized vacuum tube in which images are produced when an electron beam internal to the tube is scanned back and forth across a phosphorescent surface on the inside front of the tube. Color CRT's have phosphor screens using multiple beams of electrons to display millions of colors. The CRT itself appears in the unit as a funnel shaped, leaded glass tube, typically with a metal frame inside. Most CRT's contain lead, which is well known to be a contaminant in many instances, and some CRT's can contain up to several pounds of lead, which may be in the form of lead oxide.
If the lead bearing glass is broken up and the lead oxide is exposed to an acidic environment, lead can be leached out of the glass. Because many CRT units are disposed of in landfills, those landfills may potentially be exposed to high levels of lead, which may leach to the water table and elsewhere in the environment.
In addition, the interior coatings of older television CRTs may also contain high levels of cadmium compounds, which may also be contaminants. These cadmium compounds can also be released from the CRT, and can contaminate the ground water, among other things.
CRTs may also contain various other contaminants, as shown in Table 1. It is highly desirable to avoid disposing of CRTs in a landfill by recycling the components. One method for recycling the components of the CRT is to break or shred the units into small pieces which are made of a single material, e.g., metal, plastic, or glass. The shredding can be performed by various means including automatic hammers, saws, blades or similar devices. These smaller pieces are then sorted according to material. For example, the ferrous metal components can be sorted from non-ferrous metals, plastic and glass by magnetic filtration. Other techniques may be used to sort the glass from the other components.
Based on a typical desktop computer and 14″ monitorweighing ~60 lbs. Table presented in: Microelectronicsand Computer Technology Corporation (MCC). 1996. ElectronicsIndustry Environmental Roadmap. Austin, TX.ContentActual Weight ContentRecyclingName(% of total weight)(pounds)EfficiencySilica24.8803150%Plastics22.990713.820% Iron20.471212.380% Aluminum14.17238.580% Copper6.92874.290% Lead6.29883.85%Zinc2.20461.3260% Tin1.00780.670% Nickel0.85030.5180% Barium0.0315<0.10%Manganese0.0315<0.10%Silver0.0189<0.198% Beryllium0.0157<0.10%Cobalt0.0157<0.185% Tantalum0.0157<0.10%Titanium0.0157<0.10%Antinomy0.0094<0.10%Cadmium0.0094<0.10%Bismuth0.0063<0.10%Chromium0.0063<0.10%Mercury0.0022<0.10%Germanium0.0016<0.10%Gold0.0016<0.199% Indium0.0016<0.160% Ruthenium0.0016<0.180% Selenium0.0016<0.170% Arsenic0.0013<0.10%Gallium0.0013<0.10%Palladium0.0003<0.195% Vanadium0.0002<0.10%Europium0.0002<0.10%Niobium0.0002<0.10%Yttrium0.0002<0.10%
After the glass has been sorted from the other CRT components, the glass must be sorted based upon either lead content, or upon a similar criteria which may, for example, be based on a different contaminant. Such sorting has, in the past, been largely performed by hand, and therefore is slow and prohibitively costly for most purposes. As a result, there has been a long felt, and growing, need for a system, method and apparatus which is capable of sorting such contaminated glass in a more automated fashion.